The present invention relates to a double-headed piston type compressor to compresses gas in front and rear compression chambers that are defined by double-headed pistons as the pistons reciprocate while a rotary shaft rotates.
Japanese Unexamined Patent Publication No. 7-63165 discloses a double-headed piston type compressor for a vehicle air-conditioner system. FIG. 8A illustrates a double-headed piston type compressor that is substantially identical to the one disclosed in the above Japanese reference. The double-headed piston type compressor includes a front cylinder head 101 and a rear cylinder head 102. A front discharge chamber 111A is formed in the front cylinder head 101. A suction chamber 112 and a rear discharge chamber 111B are formed in the rear cylinder head 102. The double-headed piston type compressor also includes a pair of cylinder blocks 104A and 104B that are respectively fixed to the cylinder heads 101 and 102. Thus, a housing of the above described double-headed piston type compressor includes the cylinder heads 101 and 102 and the cylinder blocks 104A and 104B. Incidentally, in FIG. 8A, the left and right sides of the double-headed type compressor corresponds to the front and rear sides thereof, respectively.
As shown in FIG. 8B, seal members 103 are placed between the front cylinder head 101 and the cylinder block 104A. Although not shown, the seal members 103 are similarly placed between the rear cylinder head 102 and the cylinder block 104B as in the front side.
Referring back to FIG. 8A, a front compression chamber 113A and a rear compression chamber 113B are respectively defined by a double-headed piston 114 in the front cylinder block 104A and the rear cylinder block 104B. A front rotary valve 117A is utilized as a front suction mechanism 115A for the front compression chamber 113A, and a rear rotary valve 117B is utilized as a rear suction mechanism 115B for the rear compression chamber 113B. The front and rear rotary valves 117A and 117B are provided on a rotary shaft 116. The front and rear rotary valves 117A and 117B respectively include front and rear suction communication passages 118A and 118B in the rotational direction. The front and the rear suction communication passages 118A and 118B periodically interconnect a shaft chamber 116a of the rotary shaft 116 and at least one of the front and rear compression chambers 113A and 113B in a suction process as the front and rear rotary valves 117A and 117B synchronously rotate with the rotary shaft 116.
The shaft chamber 116a is open to the suction chamber 112 at the rear end of the rotary shaft 116. Refrigerant is introduced from an external circuit into the suction chamber 112. The refrigerant in the suction chamber 112 is introduced into the rear compression chamber 113B through the shaft chamber 116a of the rotary shaft 116 and the rear rotary valve 117B. Similarly, the refrigerant in the suction chamber 112 is introduced into the front compression chamber 113A through the shaft chamber 116a and the front rotary valve 117A.
However, since the front and rear rotary valves 117A and 117B are respectively utilized as the front and rear suction mechanisms 115A and 115B in the double-headed piston type compressor, the refrigerant gas that has been introduced from an external refrigerant circuit into the suction chamber 112 in the rear cylinder head 102 is distributed to the rear suction communication passage 118B and the front suction communication passage 118A. A gas path from the suction chamber 112 to the front rotary valve 117A is longer than that to the rear rotary valve 117B. The gas paths to the front and rear rotary valves 117A and 117B share a common part 119 of the shaft chamber 116a from the suction chamber 112 to the front end of the rear suction communication passage 118B as indicated by a double-headed arrow in FIG. 8A.
Namely, referring to both FIGS. 8A and 8B, when the refrigerant gas flows from the suction chamber 112 toward the front and rear suction communication passages 118A and 118B in the front and rear rotary valves 117A and 117B, the refrigerant gas tends to be introduced more into the rear suction communication passage 118B in the rear rotary valve 117B than the front suction passage 118A in the front rotary valve 117A. Thus, the front communication chamber 113A lacks for the refrigerant gas so that compression ratio is relatively large. Thereby, temperature of the discharged refrigerant gas in the front discharge chamber 111A rises substantially higher in comparison to that in the rear discharge chamber 111B. Accordingly, outer circumference of seal portions 103a of the seal members 103 that seal the front discharge chamber 111A and the front compression chamber 113A from the outside of the compressor are under thermally adverse conditions in comparison to the seal members 103 seal the rear discharge chamber 111B and the rear compression chamber 113B.